Nama wrote:
> On Oct 12, 2:37 pm, Nama  wrote:
> 
>>On Oct 12, 4:56 am, m...{at}willegal.net wrote:
>>
>>
>>
>>
>>>According to my 1982 RCA SK series replacement guide a C1214
>>>transistor has
>>>an RCA replacement of a Sk3124/289 which is an NPN transistor with
>>>similar specs to
>>>2n3904.  If it is wired in correctly, I would think that it would
>>>work.  It is only connected
>>>to the color burst signal, so worst case is that the color wouldn't
>>>work.
>>
>>>Check voltages on  the inputs the each of the three resistors going to
>>>the video circuit, as well
>>>as the output.  It is easier and faster to debug these problems with
>>>an oscilloscope or logic probe than
>>>by working blindly.
>>
>>>Regards,
>>>Mike Willegal
>>
>>>On Oct 11, 12:15 pm, Nama  wrote:
>>
>>>>Hi,
>>>>I'm trying to bring a very early (serial # in the 12000's)
rev 1 Apple
>>>>II back to life. I have been using the swap method to interchange
>>>>chips from a known working apple II+ motherboard.
>>>>At first it was completely dead, and so far I have now gotten it to
>>>>beep, power light comes on, and about 50% of the time it will access
>>>>the disk drive and look for a floppy, but no video at all!
>>>>If I insert DOS 3.3 disk on the times it is looking for a disk, It
>>>>will seem to boot, and I can then do a blind IN#6 and the drive will
>>>>boot again, so I'm assuming at least some of the time the machine is
>>>>actually functioning at a basic level, However when the drive works,
>>>>or does not work seems totally random, and is probably a separate
>>>>issue.
>>>>I think my first and biggest hurdle is to get the video working. I
>>>>have replace all the IC's in the video circuit (and many
more) without
>>>>change. There is nothing on the screen at all, and It is completely
>>>>blank. I'm don't even think there is an onscreen flicker when I turn
>>>>the machine on and off.
>>
>>>>With further inspection of the video area I noticed that someone has
>>>>done a bad repair of replacing the 2n3904 npn with a
c1214(?). At this
>>>>point this seems like the likely culprit, but before I try to fix the
>>>>dodgy repair (some pad damage) I wanted to see if anyone else would
>>>>agree that this could be the suspect video part.
>>
>>>>As usual, thanks in advance
>>
>>>>Philip
>>
>>Thanks for the replies. I have gotten the apple II up and
>>running...almost. The sometimes boots from floopy, and sometimes
>>doesn't was a RAM issue. Ram replaced.
>>I still not sure exactly what the issue is with the video, but it's
>>working after I jumpered between 2n3409 {at} 14J to the single video pin.
>>Crystal clear image. so I'll need to look into that further. Thanks
>>for your suggestions on this.
>>
>>The only big remaining issue is the early rev 1 keyboard (without the
>>encoder). I have fixed a couple of these before, but this one has me
>>stumped. I have already replaced the 5 keyswitch which was smashed,
>>and now it works well. The keys that don't work are 1, 2, R, and F. K
>>is also a little intermittent, but thats an easy fix. and finally
>>pushing either the 4 key or the W key both display  'W4'...maybe there
>>is a short somewhere between these keys.
>>
>>Shorting the contacts on the rear of the board, on keys 1 or F makes a
>>1 or F appear on the screen, so I can assume the problem is just a
>>keyswitch issue. However shorting the contacts on R and 2 do nothing!
>>Maybe a dead component elsewhere is causing this.
>>
>>If anyone has any insights again, I would greatly appreciate your
>>help.
>>
>>Philip
> 
> 
> Ok...replying to myself here.
> The 'W4' issue solved itself with a couple of little twist of the
> keyboard circuit board.t. The other keys were fixed by either
> reflowing the solder to the joints, or by replacing the keyswitches
> altogether. I should let you all know that when I got the Apple II,
> the keyboard was visably bowed The keys in the middle of the keyboard
> were about 5mm lower than those on the ends. Someone had been pounding
> on those keys over the years and had bent the metal rails that keep
> the circuit board straight. With some force I straighten the railings
> (which are riveted to the board) and maybe during this process some of
> the solder connections to the keyswitches may have broken loose, could
> this be why a couple of the keys could be fixed by reflowing the
> solder.

Exactly--nice find!

The intermittent short causing the "W4" issue may return.  Careful
examination of the traces involved along their entire length--including
the connector--will likely reveal the problem so you can make sure it
is permanently fixed.

> So all fixed apart from the video issue. I don't really want to keep
> that jumper on forever, so, I'll be looking at that part again soon.
> But for the time being I'm very happy. From completely dead with
> smashed and missing keyswitches, to fully functional in less than 2
> days. The serial number for this machine is #12097, so if feels good
> to bring another early one back to life.

I don't have a schematic handy, but you may find that there is a broken
trace connecting the two points you have bridged with a jumper.  ;-)

-michael

Parallel computing for Apple II computers!
Home page: http://members.aol.com/mjmahon

"The wastebasket is our most important design
tool--and it's seriously underused."
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